There are several requirements for the performance of electrical cables used for airborne sonar. Such cables, in addition to carrying electrical signals, must support a fairly heavy transducer which is reeled into and pulled out of the water many times. Since physical orientation of the transducer is important, it is necessary that the cable be torque-balanced to avoid wind-up or spinning of the transducer while suspended. Because of the large number of reeling cycles, the cable must be strong enough to withstand fatigue stresses and should be designed to minimize damaging concentrated loads which frequently occur when the cable passes over a sheave. Additionally, it is known that such cables must dissipate very large static electricity charges and must shield the signal conductors from such charges as well as other electromagnetic interference from the helicopter. A cable which meets the above requirements is described in U.S. Pat. No. 3,843,829 (common assignee).
Recent requirements have made it necessary to design a new cable which meets the above qualifications but which operates at substantially greater depths. The cable must therefore be much longer. Since hovering time should not be substantially extended, the cable should withstand greater reeling speeds than eariler units. Also, the size and weight of the cable become more critical because of the required size of the storage reel and weight of cable to be carried on the helicopter. The size also effect hydrodynamic drag on the portion of the cable being immersed; obviously this should be minimized.